In many optical applications, it is required to provide a substrate with an anti-reflective coating. An anti-reflective coating is often realized by depositing a number of partial coatings one-atop-the-other, wherein partial coatings with a low refractive index alternate with partial coatings with a high refractive index (DE 10 2005 015 631 A1). The depositing of a plurality of partial coatings, however, requires either a relatively large amount of time if a substrate is repeatedly passed through two coating stations for the depositing of two different types of partial coatings, or highly complex equipment if the substrate is passed through a number of coating stations corresponding to a number of partial coatings in one pass.
From DE 10 2005 020 168 A1 a method for depositing an anti-reflective coating is known wherein a porous coating comprising a metal or a mixed metal oxide is deposited using a sol-gel method. The pores inside the coating cause the radiation hitting the coating at the pore borders to reflect at different angles, which results in anti-reflection. At the same time, however, the pores inside the coating also cause a reduction in the transmission which restricts the range of applications of this method.
Another alternative for reducing the interface reflection of plastic substrates has been described in DE 102 41 708 A1. With this method, a refractive index gradient coating is formed on a substrate surface by bombarding a polymer substrate with ions. Such methods, however, can frequently not be applied to extensive substrates, like, for example, plastic foils.